It is known, in case of transverse deficiency of superior maxilla, to resort to a corrective expansion therapy implemented by applying a fast expansion force of high intensity so as to cause the expansion with fracture and subsequent osteogenesis of the maxillary bone. To obtain this result use can be made, for example, of screw devices such as the one disclosed in U.S. Pat. Nos. 4,347,054 and 4,482,318, as well as WO 94/10933, and of the screw model A0620 manufactured by the same Applicant. In case of an expansion in anteroposterior direction concerning both the maxillary and mandibular bones, where no bone sutures to be expanded nor fractures are present, an operating technique of distraction and osteogenesis is applied which uses screws such as the one described in the U.S. Pat. No. 5,599,183 which refers to an apparatus for assembling a device for mandibular distraction. This type of device comprises, essentially, a plurality of orthodontic bands allowing it to be fixed to predetermined dental elements of both sides of the concerned dental arch, which bands are engaged to expansion screws located externally and sideway thereof so as to be moved away from each other by an expansion operated by rotating a screw-actuating portion by means of pin element to be inserted into holes or cavities suitably provided on a plane orthogonal to the longitudinal axis of each screw. In this way, there is obtained the distraction of the anterior portion from, for example, the posterior one.
Illustrated in FIG. 1 of the attached drawings is an apparatus of the type mentioned above, wherein (1, 10) indicate the orthodontic bands, (2) is the expansion screws, (3) refers to the acting portion of the same screws and (4) indicates the means for operating the distraction.
However, experience has shown that the operation of the screws of the type above described is very difficult to carry out owing to the small space available between the screws and the inner surface of the corresponding cheeks, and to the consequent reduced visibility for the operator who has to drive the screws.